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Researchers are now experimenting with stem cells—progenitor cells that can develop into many different types of tissue—to coax the bodies of a few individuals to heal themselves. Some of the most advanced clinical trials so far involve treating congestive heart disease and regrowing muscles in soldiers who were wounded in an explosion. But new developments are happening so quickly that investigators have come up with a new name—regenerative medicine—to describe the emerging field.
Many of the stem cells being studied are referred to as pluripotent, meaning they can give rise to any of the cell types in the body but they cannot give rise on their own to an entirely new body. (Only the earliest embryonic cells, which occur just after fertilization, can give rise to a whole other organism by themselves.) Other stem cells, such as the ones found in the adult body, are multipotent, meaning they can develop into a limited number of different tissue types.
One of the most common stem cell treatments being studied is a procedure that extracts a few stem cells from a person's body and grows them in large quantities in the laboratory—what scientists refer to as expanding the number of stem cells. Once a sufficient number have been produced in this manner, the investigators inject them back into the patient.
The bone marrow is a rich source of adult stem cells, containing both the hematopoietic stem cells that give rise to the various types of blood and the so-called mesenchymal cells, which can develop into bone, cartilage and fat. Mesenchymal cells are found in the bone marrow and various other places in the body, although whether all mesenchymal stem cells are truly interchangeable irrespective of origin is unclear.
Scientific American spoke with Mahendra Rao, director of the Center for Regenerative Medicine at the National Institutes of Health in Bethesda, Md., to get a sense of the sorts of new developments that might occur in regenerative medicine in the next five years or so.
[An edited transcript of the interview follows.]
Why is there so much excitement about regenerative medicine?
You could say that medicine up until now has been all about replacements. If your heart valve isn't working, you replace it with another valve, say from a pig. With regenerative medicine, you're treating the cause and using your own cells to perform the replacement. The hope is that by regenerating the tissue, you're causing the repairs to grow so that it's like normal.
And research into regenerative medicine has been going at a pretty fast pace.
Yes, there have been a lot of novel breakthroughs in the past few years. It seems that things are moving relatively rapidly to true translation and clinical practice. When you think about it, it usually takes 10 to 14 years to bring a drug to market. Well, the entire field of pluripotent stem cells is 14 or 15 years old. And yet, in those 15 years there are already clinical trials in place.
And if you include the non-pluripotent cells, then there are already five or six products in the U.S. and other countries. There's Provenge [for prostate cancer], Appligraf [to treat diabetic foot ulcers], Carticel [to replace knee cartilage], Gintuit [to promote healing after gum surgery] and Fibrocell is replacing fibroblasts.